1. Field of the Invention
The present invention relates generally to the art of making Al(PO.sub.3).sub.3 and more particularly to the preparation of the different chain forms of aluminum trimetaphosphate.
2. The Prior Art
Crystalline condensed aluminum phosphates are described in the literature by D'Yvoire, who identified a cycle aluminum tetrametaphosphate, the stable A-form of Al(PO.sub.3).sub.3, and four long-chain polyphosphates, the B C, D and E forms of Al(PO.sub.3).sub.3. According to D'Yvoire, these crystalline condensed aluminum metaphosphates are produced by reacting P.sub.2 O.sub.5 and Al.sub.2 O.sub.3 in a molar ratio of 4 to 15 over several hours.
U.S. Pat. No. 4,216,190 to Neely teaches a method for preparing predominantly the B-form of aluminum trimetaphosphate by the addition of ammonia to a solution of aluminum dihydrogen phosphate, Al(H.sub.2 PO.sub.4).sub.3. A white precipitate is formed, which is directly converted to B-form aluminum trimetaphosphate, Al(PO.sub.3).sub.3, by a single elevated temperature treatment.
In a study of the effects of grinding on the structure and properties of various aluminum phosphates, Tsuhako et al report mixing .alpha.-alumina and ammonium dihydrogen phosphate, and heating at 500.degree. to 550.degree. C. for 20 hours to obtain the B-form of Al.sub.4 (P.sub.4 O.sub.12).sub.3.